I have a 2007 chevy silverado the fan does not turn on when the temperature get more than 210 only if I turn the a/c on not by themselves and the relays are good any help on this thanks

chek if the electric fan is turning on when the ac is turned on

The gauge is supposed to move. Between 190 and 210 degrees. About a 1/16 to 1/4 inch movement with the needle. If it goes from middle(200 degrees) to hot(260 degrees) and back. Check the coolant level. Air pocket in the engine. Low fans come on at about 210 degrees. High fans come on at 225 degrees. High fans come on when the A/C is turned on. And it works.

This sounds like a bad coolant temp sensor that give computer false reading, check the coolant temp sensor connector and if it is good with no bad wires to connector then replace coolant temp sensor , when the computer gets a signal from temp sensor that engine is hot it turns fans on high speed to cool radiator and displays a/c turned off , if this truck does not have electric cooling fans then they wont run just explaining what happens depending on engine and cooling set up. replace coolant temp sensor and check connector.

Sounds like the engine computer is falling into the limp in mode. The best way to know if it's the computer or a sensor is to run a diagnostic test . That way any codes stored in the computer will pinpoint the problem

The thermostat circuit that controls the on/off cycles of the radiator fan motor is not working properly in that its performance is, at best, erratic. But the car is not overheating which is a plus. Will not harm car and in cold weather it will take it a tad longer for the engine to reach full operating temperature.

I would start with the coolant temp. sensor. You should be able to by pass it and make the fans come on. By pass by jumping the wires that plug into it. Here is a picture of what she looks like.

Instrument cluster - GM had problems with a part inside the cluster , Stepper motor , These faulty step motors caused the gauges to act erratically . 2003 to 2006 ! ALL GM vehicles . Just replaced a cavalier instrument cluster for what customer thought was a over heating problem .The fans come on low speed when engine temp. reaches 220 degress
The PCM commands the low speed cooling fans ON under the following conditions:
• Engine coolant temperature exceeds approximately 104.25°C (220°F).
• A/C refrigerant pressure exceeds 1447 kPa (210 psi).
• After the vehicle is shut OFF if the engine coolant temperature at key-off is greater than 101°C (214°F) the low speed fans will run for a minimum of 60 seconds After 60 seconds, if the coolant temperature drops below 101°C (214°F) the fans will shut OFF. The fans will automatically shut OFF after 3 min. regardless of coolant temperature.
The PCM commands the high speed fans ON under the following conditions:
• Engine coolant temperature exceeds approximately 107.2°C (225°F).
• A/C refrigerant pressure exceeds approximately 1824 kPa (265 psi).
• When certain DTCs set.
At idle and very low vehicle speeds the cooling fans are only allowed to increase in speed if required. This insures idle stability by preventing the fans from cycling between high and low speed.

250 TOO HOT FOR ENGINE AND TRANSMISSION. SOUND LIKE COOLING FAN CLUTCH BAD ITS FREEWHEELING NOT LOCKING UP TO DIRECT DRIVE TOO COOL ENGINE OFF BECAUSE THE FAN CLUTCH THERMOSTAT NOT WORKING THE HOT SILICONE OIL CAUSE IT TO EXPAND TO PUT RESISTANCE ON CLUTCH TO PUT DRAG ON FAN CLUTCH CAUSING IT TO LOCK IN GIVE IT DIRECT DRIVE.I WOULD STILL REPLACE THERMOSTAT AND RADIATOR PRESSURE CAP IF TEMPERATURE STILL 250 DEGREES YOUR RADIATOR AND COOLANT SYSTEM NEED FLUSHING.

sounds like you have a bad temperature sensor/fan switch usaully located on the radiator. turns on fan when coolant reaches operating temperature. when moving the ram air going thru radiator is enough to cool the engine without the fan,

With the truck running at operating temperature, squeeze your upper radiator hose. You may have to check it a couple times allowing time for your thermostat to open. Are you able to compress the hose a little when you squeeze it or does it remain stiff/solid? Your thermostat may be stuck open or even stuck closed.